Nuclear medicine techniques (such as SPECT) have the potential to become powerful new tool in imaging biological processes in small laboratory animals. With the ever increasing number of human disease models, particularly in the smaller animals such as mice and rats [Bernstein, Doetschman, Hanahan], the potential of high resolution nuclear medicine technology to contribute unique information is becoming apparent to many researchers. The critical advantage of nuclear medicine procedures is that they allow functional information to be obtained non-invasively, so each animal can be studied repeatedly. It needs to be pointed out that the obvious advantages of SPECT are accompanied by some limitations. Most importantly, SPECT images do not provide detailed anatomical information needed for localization studies. Additionally, the non uniform attenuation of gamma rays by the surrounding tissue causes image distortions and quantitative errors in reconstructed SPECT and PET images. These limitations in SPECT imaging can be overcome by combining SPECT imaging with X-ray CT imaging. The goal of the proposed effort is investigate two high resolution detector systems to allow combined SPECT/CT imaging of small animals. PROPOSED COMMERCIAL APPLICATIONS: Nuclear medicine such as siungle photon emission computed tomography, radiology, non-destructive testing, materials research, X-ray diffraction, nuclear and high energy physics research, astronomy, and geological exploration.